I have a MEC / WARWICK 3 band bass on board eq and it has an issue. when i plug in my bass guitar the active system has a lot of noise and RF interference. the signal sounds weak when compared to the passive sound? I replaced the battery and i do not see any wires disconnected from the circuit. Any help on this would be appreciated.

the voltages on the TL064 are good - the voltages on the TL062 do not look right to me but without seeing the schematic - hmmm. i would replace the TL062 and remeasure the voltages you should be getting approx 4.5 volts on pins 1,2, and 3.

You should double check the schematic for R1 - it doesn't make much sense to bias the + input through R3, then connect it to the ground.Also, pins 10 and 5 of TL 064 should get some bias from somewhere.Double also, you may have missed a resistor from pin 14 to pin 6 of TL064.

mw3_1.png

Other than that, nothing beats the old audio probe in debugging.

LATER EDIT: try to use easier to edit/view formats like png/gif/jpg, instead of pdf, when posting things not meant to be definitive.

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As Bajaman said, the first op amp has a problem. I would take out the TL062, then measure the voltage at pin 3 (in the op amp socket) and resistance from each of the pins 1 and 2 to ground. The voltage should be VR and pins 1 and 2 should have no connection to the ground. I'd also test the electrolytic caps around the op amp (C12 and the 1uF between R2 and ground).

Hallo, could someone please, post the pots for the circuits, where they connect and what value they are? I m not finding anything on google at the moment for a 3band mec preamp. I play on a warwick fortress one 5 and have always liked the sound, but I play it passive. I'd like to give it a try a the active middle cut. Thank you, Sergio

I can see the following differences between my schematic your update:- Where R4 and R12 connect, R12 on my schematic connects to the other side of R4 compared to yours. * From a technical perspective on how the circuit works I'd go with my connection.- C2 connects to the other other side of C1. * Both will work, hard to know what is correct without a PCB.- R11 value: Mine 20k, Yours 22k. * Not much to worry about there. Again, would need to be checked against a PCB. Maybe this part varied in production?- C4, C8, C9 values. Mine 10pF, Yours 100pF.* No idea what is correct. I'd have to go over my info and see how clearly I could read the values. EDIT: I can confirm these caps are 10pF. It is also clear these caps are different to C2 on the PCB. Personally I'd probably prefer the sound of 100pF. - I've got a diode on the power. * I believe this is correct as you can see it on the PCB pic I've posted.